Hairs

What is hair?
Hair is an accessory organ that provides added protection to the body. It consists mainly of a protein known as keratin. Hair is made of dead cells and gets its color from melanin, a pigment produced by melanocytes in the skin.

Where are hair situated?
The distribution of hair on the human body varies according to age and sex. Hair on the head is present since birth. After the onset of puberty, there is an increase of hair growth all over the body. Pubic hair develops in both sexes followed by hair in the armpits and the insides of the thighs. This hair is soft and smooth initially, but becomes coarse and curly as teenage follows. In males, hair on the chest, forearms and thighs develop rapidly. Abdominal hair is also seen and it slowly grows up to the pubic region in males. Men have hair on the upper lip called as the moustache and the jaw called as the beard.

Fine hair is present in the nostrils to filter out large particles of dust and foreign bodies. Hair is also present in the ears in males.

How can we describe hair?
Hairs are basically long thin strands of the protein keratin. Depending on the race of people, it may vary in color and texture. In people of Asian origin, hair is usually long, thin and black. Western races have hair that is straight, blond, orange or reddish in hue. The blacks have thick, short and curly hair, with lesser distribution on the body. The Orientals have hair that is long, thick and black.

Structure and growth of hair
Hair is made of three layers, the inner medulla, which is hollow, the outer thick, pigmented cortex and the outermost cuticle. The hair grows from a structure called as the hair follicle. This is a specialized area of the epidermis that grows into the dermis. A hair is generated from the rapidly dividing cells at the base of the follicle in the bulb. The bulb is a structure located in the dermis. The papilla under the bulb contains blood vessels that carry nutrients to the hair. Each hair follicle has specific growth phases followed by rest phases. However these phases of growth are not the same for all growing hair. Each day some hair grows, while others are shed. Hair grows at the rate of 6mm to 8mm every month.

Functions of hair
Hair has multiple functions. Thick hair on the head helps insulate the head against heat loss and protects it from the sun’s effects. Hair on the eyelashes and eyebrows protects the eye from foreign particles and direct sweat from the forehead, away from the eye.

In low temperatures, when body temperature drops, blood vessels constrict, i.e. their diameter decreases. The erector pili muscles in the dermis also contract and make the hair erect. The rigid hair traps an insulating layer of air next to the skin, which prevents the skin from getting cooler.

Hair in the nostrils prevents foreign bodies and dust from entering the nostrils and the lungs.